1. Field
The present invention relates to a capacitor-embedded printed circuit board.
2. Description of the Related Art
The various demands of the consumers are increasing regards current portable electronic devices. In particular, demands for multi-functionality, small size and light weight, fast processing speed, low cost, better portability, wireless Internet access in real time, and sophisticated design, etc., are placing a burden on developers, designers, and manufacturers to produce higher quality products.
The intensified competition is leading to rapid continuous releases of new models among different competitors, which in turn is increasing the burden on the persons involved. With the increase in variety of the functions provided by a product, the number of passive components is increasing in relation to the increase of active components, whereby the overall volume of a mobile terminal is also being increased.
In general, numerous active and passive components are mounted on the surface or surfaces of a circuit board, where many passive components are mounted on the surface or surfaces in the form of discrete chip capacitors to facilitate signal transfer between active components. In many related companies, continued development efforts are being focused on the PCB (printed circuit board) having embedded components, for high density mounting in an electronic system. The passive components embedded in the board may include resistors, condensers, and coils, which may be grouped according to the shape and form of the embedded components into conventional components, thin components, film components fabricated by printing or sputtering, and plated type components, etc. However, with the use of separate components, there is a limit in responding to the trends of lighter, thinner, and simpler products, and there may be problems in terms of efficient use of space and increased costs.
Among the types of passive components embedded in a board, numerous attempts are being made at embedding the thick film type (15-25 .mu.m) capacitor in a board, for which many patents are being published. The attempts are being continued, in particular, for implementing the characteristics of lightness, thinness, and simplicity in the electronic system. Methods of embedding a film type capacitor in a board include those that employ roll coating, sputtering, and sheet lamination, etc., where sheet lamination has been found effective in decreasing thickness tolerances and reducing costs.
FIGS. 1A to 1D are cross-sectional views representing a process of manufacturing a capacitor-embedded PCB by sheet lamination according to the related art.
As shown in FIG. 1A, inner electrodes 12a, 12b may be formed on either side of a core layer 11. In FIG. 1B, a leveling process may be performed using coating ink 13a, 13b. Afterwards, as illustrated in FIG. 1C, a pair of copper clad laminates 14a, 14d, in each of which a dielectric layer 142a, 142b and a copper layer 141a, 141b are stacked together, may be stacked such that the dielectric layers 142a, 142b face the coating ink 13a, 13b. In FIG. 1D, the copper layers 141a, 141b may be removed to form outer electrodes 15a, 15b. 
In the capacitor-embedded PCB according to the related art, as illustrated in FIGS. 1A to 1D, if there are irregularities in the surface or surfaces of the coating ink 13a, 13b, portions of the dielectric layers 142a, 142b may fill in the irregularities, causing the dielectric layers 142a, 142b to have a non-uniform thickness, and affecting the reliability of the capacitor.
In addition to the above, there are several other methods for implementing an embedded capacitor. The decoupling capacitor, which serves to stabilize the power supply, may not require sensitive values with regard to capacitance tolerance. However, for the RF matching capacitor, not only the stability to temperature, but also the value of the capacitance itself, may require high tolerance. In recent times, the method of implementing an embedded capacitor using RCC type capacitor laminates is receiving much attention, as it allows relatively adequate thickness control. However, the material for the RCC type embedded capacitor provides very low stackability, so that an additional process may be required for leveling the surface on which the material for the RCC type embedded capacitor is stacked. A structural problem with the material for such RCC type embedded capacitor is that, in spite of the additional process of leveling the stacking surface, there can be high thickness deviations in the dielectric layers of the capacitor material with respect to the Cu pattern thickness or resin thickness at the stacking surface, leading to defects such as delamination at the stacking surface in severe cases. Also, the tenting method employed in forming the electrodes of the capacitor entails a limit to reducing deviations in capacitance in the overall embedded capacitor, as there can be high deviations in the electrodes of the embedded capacitor due to the etching process.